Nonwoven fiber webs or structures frequently consist of a random yet homogeneous agglomeration of long and short fibers. Long fibers are fibers of both natural and synthetic origin that are suitable for textiles. They are longer than 0.25 inches and generally range between 0.5 and 2.5 inches in length. Short fibers are suitable for paper-making and are generally less than about 0.25 inches long, such as wood pulp fibers or cotton linters.
Nonwoven web products may also comprise particulate matter, such as absorbent powders, in combination with long and short fibers. For example, a highly absorbent powder or fiber can be held within a pocket of fibers having good water moving properties.
There are many different methods and devices useful for making nonwoven webs or structures. Conventional carding or garnetting methods produce nonwoven fiber webs, but these are generally limited to textile length fibers. Methods of forming nonwoven web products in pockets, i.e., having a non-uniform cross section, a predetermined topography, or sharply defined edges are also known.
The "Rando-Webber" process may be used to make nonwoven webs. In this process, pre-opened textile fiber material is delivered to a lickerin that opens the fibers further, and introduces them to a high-velocity low-pressure air stream. The fibers are randomly deposited on a condensing screen to form an isotropic web. While a uniform web of textile fibers can be obtained, this process is not suitable for use with short fibers or blends of long and short fibers.
U.S. Pat. No. 3,512,2I8 of Langdon describes two lickerins and rotary feed condenser assemblies arranged in parallel one after the other. Isotropic nonwoven webs are formed with this apparatus by feeding fibers deposited on a condenser mat to the lickerins, where the fibers are individualized. A single airstream is divided into two parts and acts to doff the fibers from the lickerins and deposit them onto a suction box, where the web is formed. This method cannot be used to homogeneously blend two streams of fibers.
In U.S. Pat. No. 3,535,187 of Wood there is described apparatus for producing a layered web of randomly oriented fibers joined at the interface of adjacent layers by a small zone of textile length fibers extending across the interface. Wood's device provides individualized fibers which are deposited on a pair of cylindrical condenser screens by a pair of respective lickerins acting in cooperation with high speed turbulent air streams that move faster than the lickerin in order to doff the fibers. However, the air speed must also be controlled so that the fibers do not forcibly impact on the condensers. The condenser screens are positioned closely adjacent to one another and the layers of fibers on the condensers are compressed between the condensers to form a composite nonwoven web with some blending at the interface between layers. As a result, there is no substantial fiber mixing zone adjacent to the condensers, and the intermixing of fibers is minimal.
One way of making a nonwoven web consisting of a mixture of randomly oriented long and short fibers uses a milling device to individualize short fibers and a lickerin to individualize long fibers. The fibers are mixed in a mixing zone, and the mixture is deposited on a condenser to form a nonwoven web. Though randomly oriented, the mixed fibers are stratified rather than homogeneously blended. The long fibers predominate on one side of the web and the short fibers predominate on the other. In addition, undesirable clumps of fibers or "salt" occur in this web product, because the mill does not completely individualize the short wood pulp fibers.
Another method used to make webs of mixed and randomly oriented long and short fibers introduces pre-opened long and short fibers to a single lickerin for individualization. However, the optimum lickerin speeds for long and short fibers are different. To prevent the degradation of long fibers, this device must operate at the slower speed that is optimum for long fibers. As a result, the speed and throughput of the device is compromised.
Methods and devices which produce a blend of long and short fibers without clumps or salt are disclosed in U.S. Pat. No. 3,772,739 of Lovgren. Lovgren provides for the separate and simultaneous individualization of each type of fiber on separate lickerins, each operating at an optimum speed for the fiber it opens. For example, long fibers such as rayon are supplied to a lickerin operating in the neighborhood of 2400 rpm. Pulpboard is supplied to a lickerin operating in the neighborhood of 6000 rpm, a speed that would damage long fibers. The fibers are doffed from their respective lickerins by separate air streams and are entrained in the separate air streams. These streams are subsequently mixed in a mixing zone in order to blend the fibers. The homogeneous blend is then deposited in a random fashion on a condenser disposed in proximity to the mixing zone. While the Lovgren apparatus is useful, it does not lend itself to the preparation of a wide variety of webs.
Another method of producing homogeneous blends of 5 fibers is disclosed in commonly owned U.S. Pat. No. 3,740,797 of Farrington. Farrington discloses a method and machine wherein supplies of fibers are fed to oppositely rotating parallel lickerins, which are operated at respective optimum speeds to produce individualized long and short fibers. The individualized fibers are doffed from the lickerins by centrifugal force and by high velocity air streams directed against any fibers tending to cling to the lickerin structure. The individualized fibers from each supply are entrained in their respective air streams and are impelled toward each other at high velocities along trajectories that terminate in a mixing zone, where at least a portion of the fibers from each supply may be blended. A suction actuated condensing means communicates with the mixing zone so that the blended fibers are deposited on a condenser screen to produce an isotropic web of fibers. This screen is moved in a direction, i.e. the "machine direction," which is perpendicular to the axis of the lickerins. In addition, a baffle can be interposed between the air streams to control the degree of mixing and the respective location of the long and short fibers in the composite web.
It would also be advantageous to provide composite web structures having a non-uniform cross section or predetermined topography comprising zones of different fiber or particulate materials and blends thereof. For example, a method and apparatus for making nonwoven structures having selectively absorbent properties along the product's cross-section is desirable, as in the case of hygiene products such as sanitary napkins. It is particularly desirable to provide for blended composite structures having predetermined shapes with sharply defined edges.
Methods and machines for making nonwoven fluff pulp pads and pre-shaped absorbent products are known, but do not provide for selective blending and layering of pulp, textile, and particulate materials. Conventional pocket-forming devices can process only one material, usually pulp, and cannot be readily modified to provide uniformly blended pads because of the complex geometry inherent in the use of hammer mills or disc mills and cylindrical product-forming surfaces. Typical of these conventional devices are machines available from Winkler & Dunnebier Maschenfabrik and Curt G. Joa, Inc. See, for example, U.S. Pat. Nos. 4,560,379 and 4,598,441 of Stemmler. [owned by W&D]. PCT Application No. WO 85/04366 of Johnson et al. is also of interest. Johnson teaches the use of fiber-receiving molds disposed on a continuously rotating drum selectively provided with a vacuum. Other foraminous drum arrangements having circumferential cavities are taught by U.S. Pat. No. 4,592,708 of Feist et al. and U.S. Pat. No. 3,518,726 of Banks.
An early method of making sanitary napkins is disclosed in U.S. Pat. No. 2,073,329 of Winter. Winter teaches that patches of loose cotton fibers may be blown down onto a gauze-like material at regular intervals in cooperation with a suction means. Then pads of absorbent material may be placed over the cotton patches, and the gauze folded and cut at regular intervals to make the napkins. The loose cotton fibers are directed to the surface of a moving wheel having spaced and screened suction inlets adapted to receive and condense the cotton fibers in uniform patches. The Winter process requires several time-consuming and independent steps, followed by the assembly of the composite structure from its component structures. It does not provide for a composite shaped and layered structure formed by blending one or more fibrous and/or particulate materials in an integral operation.
U.S. Pat. No. 2,949,646 of Clark is also representative of the prior art, and sets forth the problem of providing three-dimensionally shaped structures having sharply defined edges. Clark recites a prior art method wherein fibers are deposited continuously from an entraining air stream onto a continuously moving foraminous belt provided with suction. The belt is partially masked in order to provide deposition and condensation of fibers into a web having the desired shape. Clark notes that this method is disfavored because of the leakage of fibers from the masked to the unmasked regions of the belt, resulting in non-uniform layers. The prior use of pans to catch fibers deposited by gravity is mentioned by Clark, as is a method of cutting webs to desired shapes, or separating webs using caul plates.
The improvement of the Clark invention over the prior art is a fiber depositing head whereby unblended web structures having contoured edges are made by entraining previously individualized fibers in a circular path within a circular housing, delivering uniform volumes of entrained fibers to a moving collecting wall through openings in a foraminous separating wall of the housing, and forming a continuous web from the delivered fibers over collecting or masking members on the collecting wall. A clean separation of the continuous web into individual mats is achieved by a trough arrangement on the collecting wall, which trough separates adjacent collecting members and prevents leakage of fibers onto the collecting members by trapping excess fibers. A means for separating the masked collecting members from the end-product is also described.
A number of absorbent articles, and methods and machines for making them, are disclosed in the patents of Kolbach, U.S. Pat. Nos. 3,846,871; 3,860,002; 3,973,291; and 4,016,628. The '002 and '628 patents relate to adhesively bonded composite structures having a medial portion of greater basis weight than flanking end and side portions. These structures are obtained by providing discrete zones of relatively high and low suction on a foraminous forming surface.
The '871 and '291 patents describe a moving pad forming assembly having spaced, three-dimensional fiber-receiving compartments separated by air-impermeable regions. Each compartment has the shape of the desired end-product and is provided with a foraminous lower surface and movable air-impermeable side walls. Individualized fibers are provided to the compartments, which in turn communicate with a fiber-entraining suction means. Selective masking of the suction means can be used to influence the density and weight of material collected within regions of each compartment, and different air-suspended fibers are deposited to different compartment sections at different, non-overlapping, times to achieve different weight and density zones within each compartment.
U.S. Pat. Nos. 3,939,240 and 4,005,957 to Savich disclose a method and an apparatus for forming fibrous pads. Savich teaches a continuously driven condenser roll having three-dimensional foraminous cavities about its periphery. Each cavity is provided with a vacuum and is brought into communication with a pad forming region that is supplied with air-suspended fibers. The fibers are deposited within the cavity and form a layer, after which each layer is removed from its cavity as a pad by another vacuum cooperating with a proximate downstream transfer conveyor. The opening into each cavity has a smaller surface area than the surface area within the cavity, so that the resulting pads are consolidated within the cavity, resulting in an increased basis weight, rather than an advantageously shaped and sharply defined composite web structure.
The prior art does not provide discrete composite nonwoven structures having predetermined shapes and consisting of layers and/or vertical zones comprising blends of long fibers, short fibers and/or particulate matter. A method and apparatus capable of providing these structures is unknown, and in particular the prior art methods do not teach a means of producing such structures in a single continuous operation.